Method and apparatus for cementing offshore wells

ABSTRACT

Method and apparatus for supporting the casing string and permitting its rotation during well cementing operations carried out from a floating drilling vessel. The apparatus includes an outer housing having an opening extending vertically through it which is normally mounted atop the subsea wellhead assembly. An inner member is supported within the outer housing and is rotatable with respect to it. This inner member has a central bore coaxial with the opening in the housing. At least one hydraulically extensible member is connected to the inner member and serves to anchor a casing string extending through the bore to the inner member. Remotely actuated means are also provided for introducing hydraulic fluid into the inner member to extend or retract each of the extensible members.

Waited States Patent 2,564,] 19 8/1951 Mathews, Jr. et all. 173/166 3,023,012 7/1962 Wilde 277/31 3,032,125 5/1962 Hiser et al 175/7 ABSTRACT: Method and apparatus for supporting the casing string and permitting its rotation during well cementing operations carried out from a floating drilling vessel. The apparatus includes an outer housing having an opening extending vertically through it which is normally mounted atop the subsea wellhead assembly. An inner member is supported within the outer housing and is rotatable with respect to it. This inner member has a central bore coaxial with the opening in the housing. At least one hydraulically extensible member is connected to the inner member and serves to anchor a casing string extending through the bore to the inner member. Remotely actuated means are also provided for introducing hydraulic fluid into the inner member to extend or retract each of the extensible members.

PATENTED mm m 3528504 SHEET 1 [IF 2 INVENTORS MARK A. CH/LDERS GEORGE H. BRUCE Z4... KW

ATTORNEY PATENTED aim an 3 .604

sum 2 UF 2 METHOD AND APPARATUS FOR CEMENTING OFFSHORE WELLS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the cementing of casing in offshore wells and is particularly concerned with apparatus which supports the casing string and permits its rotation during cementing operations carried out from a floating drilling vessel.

2. Description of the Prior Art Cementing the casing string within the borehole is an important operation in the completion and testing of wells drilled for the production of crude oil and natural gas. A successful cement job surrounds the casing string with a sheath of cement that bonds the pipe to the adjacent formations. In this way, the formations behind the pipe are segregated from one another. In the event of improper bonding or discontinuities in the cement sheath, it is difficult and frequently impossible to isolate specific zones for testing or production. Generally, the only remedy in such cases is to perforate the casing adjacent the zone of interest and then squeeze cement through these perforations into the annulus behind the pipe to seal off the zone. Squeeze cementing in an onshore well is an expensive and uncertain remedy. In an offshore operation carried out from a floating drilling vessel, the costs of squeeze cementing are multiplied manyfold. It is thus even more important to achieve a successful primary cement job in the offshore well.

It has been recognized that the likelihood of a successful primary cement job can be substantially increased by either rotating or reciprocating the casing string during placement of the cement. If this is done, the cement will more effectively displace the drilling mud from the annulus. Accordingly, in cementing operations carried out in onshore wells and in those offshore wells drilled from bottom-founded platforms, these techniques have enjoyed widespread use. Because of the limitations of existing equipment, however, such techniques have been used to only a limited extent in cementing operations conducted from floating drilling vessels.

In floating operations, the wellhead is located on the ocean floor. The casing string is suspended from the subsea wellhead by a casing hanger that rests in a bowl within the wellhead. To rotate or reciprocate the casing string while cementing, the casing string must be raised sufficiently to permit the hanger to clear the wellhead; otherwise, the sealing surfaces between the casing hanger and the wellhead will be damaged or destroyed. The clearance must be sufficient to allow for the oscillations of the casing string caused by motion of the vessel which supports the casing string. If the casing becomes stuck in this upraised position so that the hanger will not seat within the wellhead, it may jeopardize the whole operation. Attempting to land the casing string in the wellhead in such an eventuality requires cutting the casing string and fishing for the portion remaining in the hole. This is a rislry, costly, and timeconsuming operation that may result in the abandonment of the well. It will therefore be apparent that a need exists for improved apparatus that will overcome the problems presently associated with moving the casing string during cementing operations carried out from floating vessels.

SUMMARY OF THE INVENTION This invention provides a subsea rotating cementing head which at least in part alleviates the problems outlined above. This cementing head includes an outer housing having an opening that extends through it and means for connecting the assembly to a subsea wellhead assembly. An inner member is rotatably supported within the housing and has a bore aligned with the opening through the housing. Means are provided on the inner member for anchoring a string of pipe extending through the bore. Such means may include at least one hydraulically extensible member. Remotely operable means are provided for activating the anchoring means. These may include means for introducing hydraulic fluid to one or more extensible anchor members to extend or retract them.

During cementing operations, the rotating head of the invention is normally mounted on the wellhead assembly on top of the blowout preventer stack. The casing string is then positioned within the rotating head so that the casing hanger is spaced a short distance above the wellhead. Thereafter, the casing string is anchored to the inner member, preferably by means of hydraulically extensible anchor members, and is free to rotate with respect to the outer housing. The casing string is normally rotated by a power sub or casing tongs aboard the vessel.

Since the cementing head supports the casing string during rotation, it prevents vessel motion from being imparted to the casing string. The distance between the casing hanger and the wellhead can thus be quite short so that if the casing becomes stuck during cementing operations, the elasticity of the casing string will permit the casing hanger to be landed in the wellhead. It will therefore be apparent that the apparatus of the invention has significant advantages over apparatus available heretofore.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. l is an elevation view of a floating drilling vessel using the apparatus of the invention to permit rotation of a casing string being cemented within a borehole.

FIG. 2 is a cross-sectional elevation view of a rotating cementing head constructed in accordance with the invention.

FIG. 3 includes a series of schematic elevation views depicting the application of the apparatus of FIG. 2 in cementing a string of casing within a borehole.

FIG. 3A shows the casing string in its initial position with the casing hanger landed within the wellhead. In FIG. 3B the casing string is upraised and is anchored within the cementing head for rotation during the cementing operation. FIG. 3C depicts the casing string after it has been cemented. The string is still in its upraised position, but the anchor members have been retracted. In FIG. 3D the casing string has been lowered until the casing hanger lands within the wellhead. FIG. 3E shows the running string disconnected from the casing string for retrieval aboard the vessel.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 depicts a floating drilling vessel using the apparatus of the invention to permit the rotation of a casing string being cemented within a borehole. Vessel lll having a central well 13 extending vertically through its hull is shown floating on a body of water 15. The drilling equipment aboard the vessel includes a derrick 17, a crown block 119, cables 20 and traveling block 211, a running string 23, and a casing string 24!. A marine riser 25, which may have an upper ball joint 27 and a lower ball joint 29, is suspended from the vessel by means of tensioners 311. A telescoping slip joint 33, normally mounted in the riser string near its upper end, compensates for movement of the vessel relative to the borehole $9. The wellhead assembly on the ocean bottom includes a wellhead 35 mounted on conductor pipe 37, a blowout preventer stack 3%, and guide posts all. The rotating cementing head 42 is preferably mounted between the blowout preventer stack and the marine riser. Cement may be pumped through flexible hose 43 to swivel 4l5 and then down running string 23 to the bottom of the borehole. It returns to the surface through annulus 511 formed between the casing string 24 and the wall of the borehole.

With the casing in the hole and the remaining equipment assembled as depicted in FIG. 1, cementing operations are initiated by pumping cement from tanks, not shown, into the flexible hose. The cement slurry travels through the swivel and down the running string and easing string, displacing the mud contained within the borehole up through the annulus, wellhead, blowout preventer staclt, and riser string to the surface. The casing, which may be of any size up to the diameter of the blowout preventer, is supported rotatably within the cementing head during the cementing operation. The running string,

which may consist of easing or drill pipe, extends from the top of the anchored casing string upwardly through the riser string to the surface. Rotary motion is imparted to the running string and thus to the entire casing string by means of rotary table 55. Similarly, the string could be rotated by a power swivel or power tongs aboard the vessel.

FIG. 2 is a cross section of the rotating cementing head of the invention. Also shown is'a running tool 101, typical of those commercially available, that is slotted as indicated by reference numeral 102 to permit hydraulically extensible members within the cementing head to engage and thus anchor the casing string within the cementing head.

The hollow, substantially cylindrical outer housing of the cementing head is designated by reference numeral 102. Central opening or well 104 extends through the housing. End connections 105 and 107 are compatible with the corresponding connections on the blowout preventer stack and marine riser and may comprise flanges, clamps, or the like. The interior of the outer housing includes a somewhat cylindrical recess 109. A circular slot 111 in the lower interior of the outer housing receives circular bearing race 113. Main thrust bearings 115 rest on the bearing race and may, for example, be cylindrical roller bearings. Another circular slot 117 in the side of the interior of the housing receives circular side thrust bearing race 119. Side thrust bearings 121, which may, for example, also be cylindrical roller bearings, ride in the slot on race 119. These thrust bearings permit inner member 123 to rotate with respect to the housing and transmit the load carried by the inner member to the housing. Since the diameter of the housing may be much larger than that of the casing or riser string, the stress level on these bearing surfaces can be minimized.

The inner member may also be hollow and cylindrical. A bore 125 normally extends vertically through the inner member and may be coaxial with the opening or well extending through the housing.

Means connected to the inner member for anchoring a string of pipe that extends through its bore may include at least one hydraulically extensible anchor member that may be extended into the bore and retracted therefrom. The extensible anchor member shown, 127, resides within a chamber formed by hydraulic cylinder 129, passage 131, and recess 133. As shown in H6. 2, one end of the member forms hydraulic piston 135, which is slidably mounted within hydraulic cylinder 129. Seal 136 prevents hydraulic fluid from escaping between the piston and cylinder. The piston is shown integrally connected to engaging member 137, which forms the outer end of the support member, by means of connecting rod 139, Seal member 141 surrounds the connecting rod where it extends through the neck preventing any leakage of hydraulic fluid. The engaging member shown, dog 137, has its upper edge tapered to form a secure seat for the running tool. The lower portion of the outwardly extending face of the dog is tapered to correspond with the tapered portion of the running tool just below slotted section 102. A wiper seal 143 may be mounted on the lower surface of the dog to prevent the buildup of foreign material on the sliding surface of recess 133. While the means for anchoring the casing string to the inner member described comprises hydraulically extensible members, it will be apparent that other means would also be suitable.

Means for introducing hydraulic fluid into the inner member to extend the anchor members may, for example, include line 144 leading to inlet port 145, and line 146 leading to outlet port 147. Ports 145 and 147 extend through the housing and permit the introduction and withdrawal of hydraulic fluid. Seals 149, 151, 152, and 153 between the housing and the inner member, prevent the escape of hydraulic fluid to vertical well 125 when the device is actuated. These seals are not required to hold pressure during rotation of the pipe. Thus, fluid introduced through port 145 will go through passage 155, between the housing and inner member, and then through port 157 in the inner housing to the intake side of the piston in recess 129. Similarly, hydraulic fluid may be expelled from the opposite side of this piston through port 159 which extends through the upper wall of the inner member. it will then be routed through passage 161 between the housing and the inner member and out port 147. Hydraulic fluid accumulators, such as 163 and 165 shown connected to line 144 and line 146, respectively, may be located in the hydraulic system in close proximity to the cementing head. If it is desired to employ a fluid to lubricate the bearings that is different from the hydraulic fluid, a seal such as the circular seal designated 152 may be employed to segregate one fluid from another. While the fluid courses have been described in relation to extending the anchor member, it will be apparent that when the anchor member is to be retracted the fluid will travel in the opposite direction.

Prior to actuating the apparatus shown in FIG. 2, the casing string is normally positioned within the device so that the slot in the running tool is slightly below the extensible support members. Hydraulic fluid is introduced through port 145, passage 155, and port 157 into cylinder 129. Its introduction is continued until the piston, acting through connecting rod 139, extends the dog contained in recess 133 into the bore and into contact with the running tool. With the anchor members thus partially extended, the casing string is lifted upwardly relative to the rotating cementing head until the dog extends into the slot in the running tool. Accumulator 163 may be used to provide a large volume of pressurized hydraulic fluid in close proximity to the tool so that the dogs will extend rapidly. Once the dogs are extended into the slot, the running tool and attached casing are lowered until the entire weight of the casing string rests upon the extended anchor members. The casing string may then be rotated. This in turn causes the inner member, which is connected to the anchor member, to rotate with respect to the housing on thrust bearings and 121 which transmit the weight of the entire casing string to the housing. The load transferred to the outer housing is passed downwardly through the blowout preventer stack to the wellhead assembly mounted on the ocean floor.

When cementing operations have been completed, hydraulic fluid is introduced through port 147, passage 161 and port 159 into cylinder 129, so as to apply a force to the piston. This tends to retract the extensible supporting members. The casing string is then raised, relieving the weight acting on the extended engaging members and permitting them to retract into their recesses. Hydraulic fluid accumulator may be employed to cause the dogs to snap back into their recesses. In the event that the extensible members should fail to retract hydraulically, the casing string and running tool may be lifted a short distance to mechanically retract them. The tapered surface just below the slot on the running tool will engage the tapered surface on the face of the dog, which is in contact with the running tool, and drive the dog back into its recess. Accumulator 165 will receive the hydraulic fluid driven out of cylinder 129, thereby preventing a rapid buildup of hydraulic pressure which might otherwise destroy the seal members. Failsafe operation may also be insured by spring biasing the extensible anchor members. With the anchor members retracted, the casing may be carefully lowered and the hanger seated within the wellhead.

The sequence of operations involved in cementing a well from a floating drilling vessel while using the apparatus of the invention is shown schematically in FIG. 3. The wellhead 211 is attached to a submerged bottom, not shown. Hanger 213 and running tool 215 are run on running string 217, separated from one another by a distance selected so that the hanger will be just above the wellhead when the extensible anchor members engage the slot in the running tool. Mounted on top of the entire wellhead assembly, atop the blowout preventer stack, is rotating cementing head 219, the details of which are not shown. The extensible anchor member is designated as 221. FIG. 3A shows the apparatus in what is normally its initial position. The hanger is seated in the wellhead and the slot in the running tool is located somewhat below the level of the anchor member in the rotating cementing head. With the equipment in this position, the anchor member is partially extended so as to contact the upper portion of the running tool. Then, as shown in H6. 3B, the running string, running tool, hanger, and casing string are lifted upwardly relative to the wellhead and cementing head, so that the anchor member will fully extend into the slot in the running too]. The weight of the casing string is then transferred to the anchor member, cement is circulated through the casing string, and rotation of the pipe is begun. Upon completion of the cementing operations, the entire string is lifted upwardly a short distance and the anchor member is retracted into the cementing head, as shown in FIG. 3C. The running string, running tool, hanger, and casing are then lowered from the drilling vessel until they assume the position shown in FIG. 3]), with the hanger seated again in the wellhead and the running tool resting below the rotating cementing head. The running string and running tool are then disconnected as shown in FIG. 3E and withdrawn from the hole.

What is claimed is:

1. Apparatus for controlling vertical movement of a pipe string extending into a subsea wellhead from a floating vessel which comprises:

a. a hollow, cylindrical outer housing having a central well extending vertically therethrough and provided with means near the lower end for mounting said housing near the upper end of a subsea wellhead assembly;

b. a hollow, inner cylindrical member free to rotate within said housing and having a central bore extending vertically therethrough that is coaxial with said well through said housing, said inner member having at least one lateral chamber extending outwardly from said central bore;

c. means within said lateral chamber including an outwardly extensible member for engaging and holding a pipe string extending through said housing and inner cylindrical member, while permitting the passage of fluids through said inner cylindrical member; and

(1. means for introducing hydraulic fluid into said chamber to extend and retract said extensible member.

2. The apparatus defined by claim 1 wherein said hydraulically extensible member further comprises:

a. a piston;

b. an engaging member having a tapered upper surface and a tapered outer face; and

c. a connecting rod connecting the said piston to said engaging member.

3. Offshore cementing apparatus comprising:

a. a hollow outer housing having a central bore and having at least one port extending through the wall of said houss;

b. at least one bearing mounted within said housing;

c. an inner member rotatably supported within the housing by said bearing and having a central bore coaxial with that of the housing, said inner member including a hydraulic cylinder having an inlet and an outlet port extending through the wall thereof, a recess open to said central bore, and a passage connecting said cylinder and said recess;

d. an anchor member mounted within said inner member and slidable therein, said anchor member including a piston within said hydraulic cylinder, a connecting rod extending through said passage, and an engaging member residing within said recess; and

e. means for hydraulically extending and retracting said anchor member, said means including at least one hydraulic accumulator and at least one seal member positioned between said inner member and said housing, whereby hydraulic fluid from said accumulator may be passed through the ports in said housing and said inner member introduced into the hydraulic cylinder.

t. A method of controlling vertical movement of a pipe string extending into a subsea wellhead from a floating vessel which comprises; h

a. lowering the pipe string Including a hanger into the well from a floating vessel until the hanger is positioned above and in close proximity to a subsea wellhead;

b. actuating an anchoring device positioned in close proximity to said subsea wellhead to engage and anchor said pipe string against vertical movement while permitting said pipe string to freely rotate and permitting the passage of fluid between said pipe string and said anchoring device; and

c. thereafter rotating the pipe string.

5. Apparatus for controlling vertical movement of a pipe string extending into a subsea wellhead from a floating vessel which comprises:

a. an outer generally cylindrical housing provided with means near the lower end for mounting said housing near the upper end of a subsea wellhead assembly;

b. an annular, generally cylindrical member concentrically positioned within said housing and free to rotate therein;

c. means within said annular member for engaging and holding a pipe string extending through said housing and annular member, while permitting the passage of fluids through said annular member; and

d. means for actuating said means for engaging and holding said pipe string.

6. The apparatus defined by claim 5 wherein said engaging means includes at least one hydraulically extensible anchor member.

7. Apparatus as defined by claim 6 wherein said actuating means includes means for introducing a hydraulic fluid into said engaging means to extend and retract the said hydraulically extensible member.

t at: t l 1? 

1. Apparatus for controlling vertical movement of a pipe string extending into a subsea wellhead from a floating vessel which comprises: a. a hollow, cylindrical outer housing having a central well extending vertically therethrough and provided with means near the lower end for mounting said housing near the upper end of a subsea wellhead assembly; b. a hollow, inner cylindrical member free to rotate within said housing and having a central bore extending vertically therethrough that is coaxial with said well through said housing, said inner member having at least one lateral chamber extendIng outwardly from said central bore; c. means within said lateral chamber including an outwardly extensible member for engaging and holding a pipe string extending through said housing and inner cylindrical member, while permitting the passage of fluids through said inner cylindrical member; and d. means for introducing hydraulic fluid into said chamber to extend and retract said extensible member.
 2. The apparatus defined by claim 1 wherein said hydraulically extensible member further comprises: a. a piston; b. an engaging member having a tapered upper surface and a tapered outer face; and c. a connecting rod connecting the said piston to said engaging member.
 3. Offshore cementing apparatus comprising: a. a hollow outer housing having a central bore and having at least one port extending through the wall of said housing; b. at least one bearing mounted within said housing; c. an inner member rotatably supported within the housing by said bearing and having a central bore coaxial with that of the housing, said inner member including a hydraulic cylinder having an inlet and an outlet port extending through the wall thereof, a recess open to said central bore, and a passage connecting said cylinder and said recess; d. an anchor member mounted within said inner member and slidable therein, said anchor member including a piston within said hydraulic cylinder, a connecting rod extending through said passage, and an engaging member residing within said recess; and e. means for hydraulically extending and retracting said anchor member, said means including at least one hydraulic accumulator and at least one seal member positioned between said inner member and said housing, whereby hydraulic fluid from said accumulator may be passed through the ports in said housing and said inner member introduced into the hydraulic cylinder.
 4. A method of controlling vertical movement of a pipe string extending into a subsea wellhead from a floating vessel which comprises; a. lowering the pipe string including a hanger into the well from a floating vessel until the hanger is positioned above and in close proximity to a subsea wellhead; b. actuating an anchoring device positioned in close proximity to said subsea wellhead to engage and anchor said pipe string against vertical movement while permitting said pipe string to freely rotate and permitting the passage of fluid between said pipe string and said anchoring device; and c. thereafter rotating the pipe string.
 5. Apparatus for controlling vertical movement of a pipe string extending into a subsea wellhead from a floating vessel which comprises: a. an outer generally cylindrical housing provided with means near the lower end for mounting said housing near the upper end of a subsea wellhead assembly; b. an annular, generally cylindrical member concentrically positioned within said housing and free to rotate therein; c. means within said annular member for engaging and holding a pipe string extending through said housing and annular member, while permitting the passage of fluids through said annular member; and d. means for actuating said means for engaging and holding said pipe string.
 6. The apparatus defined by claim 5 wherein said engaging means includes at least one hydraulically extensible anchor member.
 7. Apparatus as defined by claim 6 wherein said actuating means includes means for introducing a hydraulic fluid into said engaging means to extend and retract the said hydraulically extensible member. 